1.\" $FreeBSD$ 2.\" $KAME: stf.4,v 1.35 2001/05/02 06:24:49 itojun Exp $ 3.\" 4.\" Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project. 5.\" All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the project nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.Dd April 27, 2001 32.Dt STF 4 33.Os 34.Sh NAME 35.Nm stf 36.Nd 37.Tn 6to4 38tunnel interface 39.Sh SYNOPSIS 40.Cd "device stf" 41.Sh DESCRIPTION 42The 43.Nm 44interface supports 45.Dq 6to4 46IPv6 in IPv4 encapsulation. 47It can tunnel IPv6 traffic over IPv4, as specified in 48.Li RFC3056 . 49.Pp 50For ordinary nodes in 6to4 site, you do not need 51.Nm 52interface. 53The 54.Nm 55interface is necessary for site border router 56(called 57.Dq 6to4 router 58in the specification). 59.Pp 60Due to the way 6to4 protocol is specified, 61.Nm 62interface requires certain configuration to work properly. 63Single 64(no more than 1) 65valid 6to4 address needs to be configured to the interface. 66.Dq A valid 6to4 address 67is an address which has the following properties. 68If any of the following properties are not satisfied, 69.Nm 70raises runtime error on packet transmission. 71Read the specification for more details. 72.Bl -bullet 73.It 74matches 75.Li 2002:xxyy:zzuu::/48 76where 77.Li xxyy:zzuu 78is a hexadecimal notation of an IPv4 address for the node. 79IPv4 address can be taken from any of interfaces your node has. 80Since the specification forbids the use of IPv4 private address, 81the address needs to be a global IPv4 address. 82.It 83Subnet identifier portion 84(48th to 63rd bit) 85and interface identifier portion 86(lower 64 bits) 87are properly filled to avoid address collisions. 88.El 89.Pp 90If you would like the node to behave as a relay router, 91the prefix length for the IPv6 interface address needs to be 16 so that 92the node would consider any 6to4 destination as 93.Dq on-link . 94If you would like to restrict 6to4 peers to be inside certain IPv4 prefix, 95you may want to configure IPv6 prefix length as 96.Dq 16 + IPv4 prefix length . 97.Nm 98interface will check the IPv4 source address on packets, 99if the IPv6 prefix length is larger than 16. 100.Pp 101.Nm 102can be configured to be ECN friendly. 103This can be configured by 104.Dv IFF_LINK1 . 105See 106.Xr gif 4 107for details. 108.Pp 109Please note that 6to4 specification is written as 110.Dq accept tunnelled packet from everyone 111tunnelling device. 112By enabling 113.Nm 114device, you are making it much easier for malicious parties to inject 115fabricated IPv6 packet to your node. 116Also, malicious party can inject an IPv6 packet with fabricated source address 117to make your node generate improper tunnelled packet. 118Administrators must take caution when enabling the interface. 119To prevent possible attacks, 120.Nm 121interface filters out the following packets. 122Note that the checks are no way complete: 123.Bl -bullet 124.It 125Packets with IPv4 unspecified address as outer IPv4 source/destination 126.Pq Li 0.0.0.0/8 127.It 128Packets with loopback address as outer IPv4 source/destination 129.Pq Li 127.0.0.0/8 130.It 131Packets with IPv4 multicast address as outer IPv4 source/destination 132.Pq Li 224.0.0.0/4 133.It 134Packets with limited broadcast address as outer IPv4 source/destination 135.Pq Li 255.0.0.0/8 136.It 137Packets with subnet broadcast address as outer IPv4 source/destination. 138The check is made against subnet broadcast addresses for 139all of the directly connected subnets. 140.It 141Packets that does not pass ingress filtering. 142Outer IPv4 source address must meet the IPv4 topology on the routing table. 143Ingress filter can be turned off by 144.Dv IFF_LINK2 145bit. 146.It 147The same set of rules are applied against the IPv4 address embedded into 148inner IPv6 address, if the IPv6 address matches 6to4 prefix. 149.El 150.Pp 151It is recommended to filter/audit 152incoming IPv4 packet with IP protocol number 41, as necessary. 153It is also recommended to filter/audit encapsulated IPv6 packets as well. 154You may also want to run normal ingress filter against inner IPv6 address 155to avoid spoofing. 156.Pp 157By setting the 158.Dv IFF_LINK0 159flag on the 160.Nm 161interface, it is possible to disable the input path, 162making the direct attacks from the outside impossible. 163Note, however, there are other security risks exist. 164If you wish to use the configuration, 165you must not advertise your 6to4 address to others. 166.\" 167.Sh EXAMPLES 168Note that 169.Li 8504:0506 170is equal to 171.Li 133.4.5.6 , 172written in hexadecimals. 173.Bd -literal 174# ifconfig ne0 inet 133.4.5.6 netmask 0xffffff00 175# ifconfig stf0 inet6 2002:8504:0506:0000:a00:5aff:fe38:6f86 \\ 176 prefixlen 16 alias 177.Ed 178.Pp 179The following configuration accepts packets from IPv4 source 180.Li 9.1.0.0/16 181only. 182It emits 6to4 packet only for IPv6 destination 2002:0901::/32 183(IPv4 destination will match 184.Li 9.1.0.0/16 ) . 185.Bd -literal 186# ifconfig ne0 inet 9.1.2.3 netmask 0xffff0000 187# ifconfig stf0 inet6 2002:0901:0203:0000:a00:5aff:fe38:6f86 \\ 188 prefixlen 32 alias 189.Ed 190.Pp 191The following configuration uses the 192.Nm 193interface as an output-only device. 194You need to have alternative IPv6 connectivity 195(other than 6to4) 196to use this configuration. 197For outbound traffic, you can reach other 6to4 networks efficiently via 198.Nm stf . 199For inbound traffic, you will not receive any 6to4-tunneled packets 200(less security drawbacks). 201Be careful not to advertise your 6to4 prefix to others 202.Pq Li 2002:8504:0506::/48 , 203and not to use your 6to4 prefix as a source. 204.Bd -literal 205# ifconfig ne0 inet 133.4.5.6 netmask 0xffffff00 206# ifconfig stf0 inet6 2002:8504:0506:0000:a00:5aff:fe38:6f86 \\ 207 prefixlen 16 alias deprecated link0 208# route add -inet6 2002:: -prefixlen 16 ::1 209# route change -inet6 2002:: -prefixlen 16 ::1 -ifp stf0 210.Ed 211.\" 212.Sh SEE ALSO 213.Xr gif 4 , 214.Xr inet 4 , 215.Xr inet6 4 216.Pp 217.Pa http://www.6bone.net/6bone_6to4.html 218.Rs 219.%A Brian Carpenter 220.%A Keith Moore 221.%T "Connection of IPv6 Domains via IPv4 Clouds" 222.%D February 2001 223.%R RFC 224.%N 3056 225.Re 226.Rs 227.%A Jun-ichiro itojun Hagino 228.%T "Possible abuse against IPv6 transition technologies" 229.%D July 2000 230.%N draft-itojun-ipv6-transition-abuse-01.txt 231.%O work in progress 232.Re 233.\" 234.Sh HISTORY 235The 236.Nm 237device first appeared in WIDE/KAME IPv6 stack. 238.\" 239.Sh BUGS 240No more than one 241.Nm 242interface is allowed for a node, 243and no more than one IPv6 interface address is allowed for an 244.Nm 245interface. 246It is to avoid source address selection conflicts 247between IPv6 layer and IPv4 layer, 248and to cope with ingress filtering rule on the other side. 249This is a feature to make 250.Nm 251work right for all occasions. 252